// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_CONTAINERS_ADAPTERS_H_
#define BASE_CONTAINERS_ADAPTERS_H_

#include <stddef.h>

#include <iterator>

#include "base/macros.h"

namespace base {

namespace internal {

    // Internal adapter class for implementing base::Reversed.
    template <typename T>
    class ReversedAdapter {
    public:
        using Iterator = decltype(static_cast<T*>(nullptr)->rbegin());

        explicit ReversedAdapter(T& t)
            : t_(t)
        {
        }
        ReversedAdapter(const ReversedAdapter& ra)
            : t_(ra.t_)
        {
        }

        // TODO(mdempsky): Once we can use C++14 library features, use std::rbegin
        // and std::rend instead, so we can remove the specialization below.
        Iterator begin() const { return t_.rbegin(); }
        Iterator end() const { return t_.rend(); }

    private:
        T& t_;

        DISALLOW_ASSIGN(ReversedAdapter);
    };

    template <typename T, size_t N>
    class ReversedAdapter<T[N]> {
    public:
        using Iterator = std::reverse_iterator<T*>;

        explicit ReversedAdapter(T (&t)[N])
            : t_(t)
        {
        }
        ReversedAdapter(const ReversedAdapter& ra)
            : t_(ra.t_)
        {
        }

        Iterator begin() const { return Iterator(&t_[N]); }
        Iterator end() const { return Iterator(&t_[0]); }

    private:
        T (&t_)
        [N];

        DISALLOW_ASSIGN(ReversedAdapter);
    };

} // namespace internal

// Reversed returns a container adapter usable in a range-based "for" statement
// for iterating a reversible container in reverse order.
//
// Example:
//
//   std::vector<int> v = ...;
//   for (int i : base::Reversed(v)) {
//     // iterates through v from back to front
//   }
template <typename T>
internal::ReversedAdapter<T> Reversed(T& t)
{
    return internal::ReversedAdapter<T>(t);
}

} // namespace base

#endif // BASE_CONTAINERS_ADAPTERS_H_
